Write iso/isohybrid on pendrive:problem

["Antispammbox-debian" <antispammbox-debian@yahoo.it>]

Hi all

Why this situations when write file iso/isohybrid on pendrive?

When write this file iso: cat debian-7.2.0-i386-lxde-CD-1.iso > /dev/sdb
on pendrive, with filesystem ext2 or Fat32, after finished to write, I can
re-format the free space present on usb.


When change file in to: isohybrid debian-7.2.0-i386-lxde-CD-1.iso

Write this file on pendrive with: cat debian-7.2.0-i386-lxde-CD-1.iso  > 
/dev/sdb
don't permit to re-format to free space on pendrive.

Gparted show: not allocated!


And why when write this file isohybrid on usb:
cat debian-live-7.2-i386-lxde-desktop+nonfree.iso > /dev/sdb

I can re-format the free space on usb?


Thanks


Regards